Detection of relative distribution patterns



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Az' fr United States Patent O 3,036,268 DETECTION F RELATIVEDISTRIBUTION PATTERNS Caldwell P. Smith, Bedford, Mass., assignor to theUnited States of America as represented by the Secretary of the AirForce Filed Jan. 10, 1958, Ser. No. 708,336 6 Claims. (Cl. 324-77)(Granted under Title 35, U.S. Code (1952), sec. 266) The inventiondescribed herein may be manufactured and used by or for the UnitedStates Government for governmental purposes without payment to me of anyroyalty thereon.

This invention relates to the detection, measurement, and correlation ofintelligence, and particularly of intelligence which manifests itself ina -series of signals (audible or visible) Whose frequency spectraestablish patterns lending themselves to electronic analysis, therebyfacilitating identification of specilic characteristics constituting thedistinguishing attributes of the intelligence undergoing examination.

The invention has utility as a means for analysis of voice signals(speech); as a means -for measuring voltageor energy distribution; as apressure pattern analyzer; as a means of measuring the distribution ofheat, or radiant energy; and in quality control and analogousoper-ations tending to follow known probability patterns.

The invention is characterized by the provision of electronic apparatuswhich-when applied to speech analysis, for example-operates to compare agradation of speech signals with a set of known coetiicients presentinga desired configuration of amplitudes constituting a reference pattern.Signals are `derived from the comparison process in such manner as toproduce a measurement, at each segment of the examined pattern, that isindicative of relative signal distribution only; that is, the indicatedresult of the pattern-matching opera-tion is independent of signalamplitudes, per se, land reilects only the overall amplitude pattern, orrelative distribution. Thus the systems accuracy is not impaired bysensitivity to the continuously varying amplitudes of successive speechsounds, the response being therefore a true measure of significantspeech content, in contra-distinction to mere sound. Morever, the degreeto which the system discriminates as between signicant speech content,fand mere sound amplitude, is controllable by simple adjustment of thedesign parameters.

Another important feature of the invention is the provision of means forrendering the pattern-matching system adjustable for the purpose ofdiscriminating on the basis of relative importance of the match atvarious segments of the pattern: critical segments of the pattern can bemade to generate a more sensitive indication of the lit than isobtainable from the non-critical segments. The relative importance ofany element of the pattern can be adjusted at will. This second-orderweighting of the pattern is independent of the generalizedpatternmatching, and can be given any desired coniiguration.

Other characteristics and objects of the invention will be indicated inthe following description of the invention as illustrated in theaccompanying drawings wherein:

FIG. 1 illustrates an average pattern for the sound of the consonant s,when uttered in ordinary speech;

3,036,268 Patented May 22, 1962 FIGS. 2, 4 and 7 are schematic diagramsof patternmatching correlator circuitry;

FIGS. 3 `and 5 are graphs showing modulator behavior; and

FIG. 6 is a -graph showing a comparison of two constant spectra.

FIG. 1 illustrates an average pattern for one particular consonantsound, as above noted. The word pattern, in this context, is intended torefer to the frequency spectrum of the sound, when uttered by onetalker, before various vowel sounds. A problem exists in presentation ofthe data in order that the differences between this consonant and otherconsonant sounds can be ascertained. The present invention solves thisproblem by normalizing the data: the vol-tage on each iilter channel iscompared with the laverage voltage for all of the filter channels, andthis ratio is expressed in de-cibels:

For the ith channel,

where e1=voltage measured on ith channel 2e=sum of voltages measured onall channels n=number of channels From this computation there arederived spectrum patterns that are independent of the signal amplitudes,thus permitting direct comparisons to be made, and average spectracomputed.

From these considerations, in turn, there can be developed an electronicpattern-matching technique to automatically classify speech sounds,which technique uses a normalizing procedure analogous to the datacomputations. FIG. 2 illustrates the basic circuitry.

The voltages to be measured appear on the set of terminals e1, e2, e3en. The pattern with which the voltages are to be compared is specifiedby the coefficients K1, K2, K3 Kn. These coeicients represent thepattern coordinates expressed in lamplitude ratios, or in decibels, withrespect .to an average value. Since they are with respect to an averagevalue,

2K=0db definition Referring to FIG. l, a pattern Ifor the average (s)spectrum would be devised 'with a set of coetlicients equal to theamount of deviation from the 0 db reference line, for each frequencychannel of the analyzing lter set. For positive values of the ordinatesshown in FIG. l, attenuators having attenuation in decibels equal to thevalue of the ordinate are required. For negative values of the ordinatesof FIG. l, amplifiers having :the specified ampliication in decibels foreach frequency channel are required. Thus the set of matching coeicientsor Ks establish a pat-tern that is the invert of the spectrum norm: itis the inverted image of :the normalized distribuation that it isdesired to mate The weighted voltage Kie, (where K, is now expressed asan amplitude ratio) is now fed to an adding circuit. In the addingcircuit the weighted channel voltage is added to the negative of theaverage voltage for all n channels. If the pattern matches, the sum ofthese two volt-ages is exactly zero. If the distribution of voltagesdoes not match the pattern specified by the Ks, the adder produces `avoltage of positive or negative polarity, having magnitude proportionalto the error.

The lconformity of the electronic pattern-matching circuitry to thegraph of FIG. 1, becomes obvious. In FIG. l, the Adata is normalized byreferring the signal in each frequency band to the average for =all ofthe bands. The electronic circuitry proceeds in the same fashion: thesumming circuit derives a vol-tage that is the sum of the voltages e1,e2, e3 en. A calibrated voltage divider divides the sum by n, where n isthe number of channels. Thus a signal is generated that is the averageof the voltage in all of the channels, and in each channel, the voltage,suitably weighted, is compared with the average voltage. The differencebetween the two signals is zero, when the distribution matches thepattern.

The output signals lfrom the various adder circuits are fed intomodulators. rIhe modulators have a control signal input, and a carriersignal input, and are characten'zed by having an output voltage that isa maximum when the control signal amplitude is zero, and the outputvoltage decreases -as a function of the amplitude of the control signal,being symmetrical in its characteristics, i.e., independent of thepolarity of the control signal, as illustrated in FIG. 3. The modulatormay have various circuit configurations, such as using vacuum tubes,diodes, saturable reactors, and other devices as are well known in thecommunications art -for achieving this type of lfunction, or, it maytake the form of the diode modulator shown in this description.

The outputs from the various modulators vare summed in a summing circuitto produce a signal Eeac proportional to the sum of the output voltagesfrom all of the modulators of the pattern. summing circuit may take anyof the various circuit configurations well known in the electronics artfor producing the sum of a set of voltages, such as pentode tubes with acommon plate resistor, triode tubes with a common cathode resistor,feedback amplifier summer, etc.

The summed signal Eea., provides a measure of correlation between theset of input voltages e1, e2, e3 etc. to the correlator, and the patternrepresented by the coefficients K1, K2, K3 etc. When the distribution ofvoltages matches the pattern specified by the set of coefficients, thesum signal Eem, will have its greatest amplitude, since for thiscondition the output from each adder circuit will be zero volts, andtherefore the output from each modulator will be a maximum. 'I'hiscondition of pattern match is independent of the absolute amplitudes ofthe voltages being measured, and is only affected by their relativedistribution or pattern.

'I'he switch S, operated by relay Ry disables the output signal whenthere is no voltage input to the patternmatching device, i.e., when2e=0. 'This disabling feature can also be provided by other features ofthe circuit, as is shown subsequently in this description.

The elements W1, W2, W3 etc. of FIG. 2 provide importance weighting tothe output signals from the various modulators. if the various elementsof the pattern represented by e1, e2, e3, etc. are all equally importantin the pattern-matching, the weightings W1, W2, W3 etc. are all made tobe equal. However, it is often true that different elements of a patternhave different relative importance, some elements being more critical asto exact magnitude, relative to the rest of the pattern, than others. Ifthe elements of the distribution specified by e1, e1, e3 etc. havevarying importance, the W elements are selected so that they are gradedin proportion to importance.

The weightings are achieved in either attenuator or amplifier circuitsin the paths of the A.C. signals from the various modulators prior tosummation. If attenuators, as implied in FIG. 2, the most importantelements are assigned the least attenuation, and the attenuation is madeinversely proportional to the importance weight- 4 ing. If amplifiers,the amplification is made proportional to importance If an analyzingsystem is constructed to use more than one pattern, there is anadvantage in selecting the set of Ws for each pattern so that2W=constant, i.e., normalizing the importance weightings. Thus themagnitude of the A.C. signal Zeal, is made equal for all patterns, forthe condition that obtains when the distribution exactly matches thepattern. This facilitates `determination of the pattern most closelymatching a given distribution.

The pattern-matching correlator shown in FIG. 2 contains severalinnovations. It represents a novel way of achieving the desiredfunction. Its output is independent of the absolute amplitudes beingmeasured, being affected only by their relative distribution. Itprovides an extremely ne measure of pattern-matching or correlation. Itprovides a means of independently adjusting the relative importance ofthe pattern-matching for the various elements of the pattern.

FIG. 4 illustrates the pattern-matching system in detail. This diagramillustrates a particular circuit configuration to achieve thepattern-matching operation illustrated in simplified form in FIG. 2.Other types of electronic devices are well known in the electronics artfor achieving the functions of modulators and adding circuits, and thesecan be substituted in the circuit of FIG. 4 without altering the basicfunction of my device, as long as the functions indicated in FIG. 2 andFIG. 3 are satislied. The specie circuit of FIG. 4 contains -additionalinnovations, that will be described.

Referring to FIG. 4, a set of voltages characterizing a distribution aredistributed on the terminals 1, 2, 3, n, where n is the l-ast terminalof the set. These voltages specify an unknown pattern that is to becompared with a reference pattern, in order to ascertain the degree ofsimilarity. The voltages e1, e2, e3 etc. are D.C. voltages; however,they may represent A.C. signals, that have been rectiiied and filtered.

The input voltages are tapped off in resistors R,i in order to derivetheir sum 2e=e1le2|e3| en. The summing circuit is contained in D.C.amplifier A and feedback resistor Ra which comprises a conventionaladding circuit well known in the electronics art. An additional functionis provided by this circuit in reversing the polarity of the 2e signal.Other adding circuits, such as pentode tubes with common plate loadresistor, triode tubes with common cathode resistor, etc. such as arewell known in the electronics art, can be substituted for the circuitshown to achieve the same function. Likewise, the reversal of polarityof the 2e signal can be achieved in the summing circuit, or in aseparate phase-reversal circuit. The configuration of FIG. 4 achievesboth of these functions.

At the output terminal of amplifier A is Igenerated a voltage that isthe negative of the sum of the voltages e1|e2-le3i en. This signal isconnected across the tapped voltage divider R, which divides the voltage2e in precise ratios.

The tapped voltage divider R acts as a reference element that can beused to establish the coefficients K1, K2, K3 Kn for any desiredpattern. Referring to the system shown in FIG. 2, there the patterncoecients are shown connected directly to the voltage terminals of e1,e2, e3 etc. However, the elements establishing the pattern coefficientscan either be in this signal path, or in the 2e path, without alteringthe operation of the device. This is easily seen, in the fact that theexpressions are exactly equivalent.

u FIG. 4 differs from FIG. 2, in that the pattern coeiclents K1, K2, K3have been shifted tothe 2e branch of the matching circuits, in order toachieve certain advannages that will be enumerated. 'Ihe mode ofoperation is basically Ithe same as previously described.

FIlhe tapped voltage divider R is constructed to provide a set ofpattern coeflicients that are specified by the voltage ratiosestablished by the taps. It thus provides a means of readily changing apattern, by merely changing the taps to which connections are made.

The voltage divider shown in FIG. 4 provides a choice of thirtydifferent possible coefficients K for each element of the pattern,spaced in equal 1 decibel increments. This represents only one of manypossible arangements. Since 1 db amplitude ratios correspond toapproximately a incremental change, the taped voltage divider R shown inFIG. 4 would permit patterns to be set up in the device having a maximumamplitude ratio of 30 decibels, with each element of the patternspecified to an accuracy of 10% or better. By providing suitable tappedvoltage dividers, the amplitude ratio, and the number and value of theincrements can be made any desired value; those specified in FIG. 4provide a convenient set for voice analysis, and their values are setforth in the table appended hereto.

As an alternative to the arrangement shown, a separate voltage dividercan be used for each element of the pattern, to achieve identicalresults.

Referring again to FIG. 4, the resistors R1 and R2 comprise the matchingcircuit in each channel. R1 and R2 have equal resistance, and serve toadd together the voltage from a particular channel, and the weightedvoltage from the tapped voltage divider. If the distribution e1, e2, e3etc. matches the set of coeflicients K1, K2, K3 etc., these two voltagesare equal in magnitude and opposite in polarity; the current owing intopoint x through R1 is exactly equal to the current iowing out of point xthrough R2, and the potential at point x is zero. `If the pattern doesnot match, the two voltages are not equal, and a difference potentialwill exist at point x, causing current to ow through one of the diodesD.

The identical diodes D from one arm of an A.C. voltage divider,consisting of the isolating capacitor C1 and the series resistor R3.Similar circuits are common to each of the matching elements. A smallA.C. carrier voltage is impressed across this voltage divider circuit,thus forming a modulator.

The non-linearity of silicon, germanium, selenium, copper oxide andsimilar diode rectifying devices is well known in the electronics art.In the forward, or conducting direction, these devices exhibit aresistance that decreases with increased current ow. The property isexploited in the diode modulator of FIG. 4.

When a D.C. current flows through either diode, the resistance of thediode decreases. The magnitude of the A.C. carrier voltage appearingacross the diodes is approximately R diode for small magnitude of E20.Thus, a decrease of the diode resistance causes the output signal todecrease. As a result, that fraction of the A.-C. carrier signalappearing across the diodes will have maximum amplitude when no D.C.current is flowing through the diodm, and will decrease in amplitudeproportional to the current that ows. Thus a modulator is formed, havingthe general characteristic shown in FIG. 3.

Other modulator circuits having the general chraracteristics shown inFIG. 3 can be substituted without altering the basic function of thecorrelator. Thus, saturable magnetic reactors, vacuum tube circuits, andother diode circuit configurations, such as are well known in theelectronics art, can be used in place of the diode modulators shown. Thecircuit of FIG. 4 uses silicon diodes as modulators, as these areconveniently simple and cornpact, and when used as modulators in mycircuit are extremely sensitive to small current changes. 1

FIG. 5 illustrative the characteristics of the silicon diodes in mymodulator circuit, showing their sensitivity to very small changes incontrol current. It also illustrates how the sensitivity of themodulator circuit can be altered at will, by altering the bias voltageon the diodes. This characteristic of variable sensitivity is utilizedin certain features of my pattern-matching correlator that will bedescribed.

As indicated above, means have been provided whereby in each channel thechannel voltage is compared with a reference pattern, established interms of a set of coefficients describing a standard distribution ofvoltages, and the degree of matching is converted automatically to anA.C. carrier signal in each channel. The A.C. carrier signals from eachmodulator are added together in a summing circuit, through the couplingcapacitors C2 and Weighting elements W1, W2, W3 etc.

The coupling capacitors C2 serve as a low-impedance path for the A.C.signals, while isolating the summing circuit for D.C., thus preventinginteraction with the pattern-matching operation.

The elements W1, W2, W3 etc. establish the relative importance of thedegree of match for each element of the pattern; the W elements may beatenuators, as shown, or amplifiers. If attenuators, the attenuation ineach channel is designed to be inversely proportional to the importanceof that channel. 'Ihe importance weighting is independent of thegener-al pattern-matching process. It offers very useful features in theautomatic analysis of voice signals by pattern-matching, and inautomatic detection.

FIG. 6 illustrates some measured differences in the frequency spectra oftwo consonant speech sounds. The average spectra of the two sounds havea maximum difference in the frequency region between 1500 and 3000cycles per second. Below 1500 cycles per second, the differences betweenthe two sounds are too small and variable to be of signilicance indiscriminating the two sounds in terms of their spectra.

The difference plot of FIG. 6 indicates the relative importance ofvarious frequencies in distinguishing the two sounds. In apattern-matching voice analyzer, discrimination of these two similarspeech sounds is facilitated by providing an importance weighting, thatwill give greatest prominence to those elements of the spectrum patternthat lie in the frequency range between 1500 and 3000 cycles per second.

Similarly, in analyzing the vowel sounds, the energy peaks, or formants,of the vowel spectra, are of much greater significance than the valleysor minima of the frequency spectra. By choosing appropriate weightings,the importance of these elements of the vowel patterns can beestablished, in a pattern-matching voice analyzer.

The pattern-matching system above described is independent of theamplitudes of the voltages e1, e2, e3 en, being sensitive only to thepattern of their distribution. However, if the incoming distributiondoes not precisely match the pattern established in the machine, errorvoltages are developed in the various channels, proporti-onal to theamount of error. These error voltages are also proportional to themagnitudes of e1, e2 etc.

If there were no compensation for this effect, the pattern sharpnesswould vary with voltage amplitudes, resulting in relatively broadpattem-matching when the sum of the voltages, Ee is small, and extremelysharp pattern-matching when 2e is large.

In some applications it may be useful to have the pattern-matchingsharpness vary as a function of the magnitude of 2e. In -otherapplications, it is useful to maintain the pattern selectively constant.FIG. 4 illustrates a method of automatically compensating for changes inpattern sharpness, that Will tend to keepy the pattern sharpnessconstant. Compensation is achieved by automatic biasing of the operatingpoints of the diode modulators.

Referring to FIG. 5, it can be observed that the diode modulators haveeither sharp or broad control characeteristics, depending on the amountof D.C. bias voltage that is applied. By tapping off a portion of the 2eand 2e signals in resistors R4 and R5, the diode modulators areautomatically biased in proportion to the magnitude of 2e. Thus anincrease in the average voltage automatically broadens the diodemodulator characteristic, to compensate for the sharpening effect thatwould otherwise occur.

Still another function is provided by the diode biasing circuit. When 2edrops to zero, the bias on the diode modulators is automatically shiftedIto an operating point such that the diodes conduct sufficiently toreduce the A.C. output signal below a threshold value, thus disablingthe system. This function replaces the use of the switch and relay inFIG. 2.

FIG. 7 illustrates a voice signal analyzer system using mypattern-matching elements for the automatic identification of speechsounds. A conventional set of speech analyzing filters and rectiiiersare used to generate a set of D.C. signals whose distribution on theterminals T1, T2, T3 etc. are related to the speech sound at eachinstant. The analyzing filters and rectifiers may be of the structureshown in my U.S. Patent 2,691,137, or of the structure shown in H. W.Dudleys U.S. Patent 2,248,089 or other sets of filters appropriate forresolving the frequency spectra of speech sounds.

Voltages appearing on terminals T1, T2, T3 etc. are added up in asumming circuit similar to that shown in FIGS. 2 and 4 to generate asignal that is the sum of the various voltages. The polarity of thissignal is reversed in a phase reversal amplifier, and the signal isdivided into precise increments on a tapped voltage divider.

A multiplicity of patterns are connected to the terminals T1, T2, etc.Each pattern is designed to correspond to the average frequency spectrumfor a particular, significant speech event, i.e., a speech sound, or aportion of a speech sound. These patterns are all of the type shown inFIG. 4. Thus a voice signal is automatically classified in terms of theset of patterns.

Following is a table showing values suitable for the tapped voltagedivider in order to establish the indicated weighting coefficients:

Weighting Coefficients K in decibels Voltage Position oi ratio Tap onR5.61 5.61 R/n 5.0 5.0 R/n 4.46 4.46 R/n 4.0 4.0 R/n 8.54 3.54 Rl'n, 3.163.16 R/IL 2.82 2.82 R/n 2.5 2.5 R/n 2.24 2.24 R/'IL 2.0 2.0 R/n 1.771.77 R/n 1. 58 1. 58 R/'rt 1.41 1.41 R/n 1.26 1.26 R/TL 1.12 1.12 R/n1.00 1.00 R/n .89 .89 R/n .795 .795 R/rt .71 .71 R/lt .63 .63 R/n .56.56 R/n .50 .50 R/n .447 .447 R/IL .40 .40 R/n .355 .355 R/n .316 .316R/n .282 .282 R/lt .250 .250R/1t .224 .224 R/'lL .200 .200 R/n .178 .178R/n In this table,

R=total resistance of voltage divider n=number of voltages or patternelements What I claim is:

l. In an intelligence identifying system, means includingfrequency-analysing lters and rectifiers multipled from a common signalsource for producing a set of D.C. voltages graduated over a rangerepresentative of the intelligence pattern to be identified, meansincluding a summing circuit receiving the rectified outputs of saidfilters for deriving a voltage that constitutes an average of all ofsaid voltages, means for reversing the polarity of said average voltage,adder means individual -to said filters, and having input connectionsfor receiving the signal content of the respective rfilters, and anadditional input connection for receiving the reversely poled aver-agevoltage signal for adding to said reversely poled average voltage aseries of amplified voltages and a series of attenuated voltages, allvoltages of said two series being complementary parts of a referencepattern of voltage distribution, modulator means in series with theindividual adder means for converting the voltage sums, derived from therespective adder means, to A.-C. signals proportional to the degree towhich said first-named pattern matches said reference pattern, means inthe paths of the respective A.C. signals for Weighting said A.C. signalsin accordance with the relative importance of the pattern segmentsrepresented thereby, and means common to the output circuits of all ofsaid weighting means for registering a value indicative of the sum ofall Said Weighted A.C. signals.

2. A system as defined in claim 1, including relayoperated switch meansresponsive to cessation of signal input to yde-activate said registeringmeans.

3. In an intelligence identifying system, means includingfrequency-analysing filters and rectifiers multipled from a commonsignal source for producing a set of D.C. voltages graduated over alrange representative of the intelligence pattern to be identified,means including a summing circuit receiving the rectified outputs ofsaid filters for deriving a voltage that constitutes the sum of all saidvoltages, means for reversing the polarity of said sum voltage, `addermeans individual to said filters, and having input connections forreceiving the signal content of the respective filters, and an-additional input connection for receiving the reversely poled averagevoltage signal for adding to precise divisions of said reversely poledsum voltage `a series of `amplified voltages and a series of attenuatedvoltages, all voltages of said two series being complementary parts of areference pattern of voltage distribution, modulator means in serieswith the individual `adder means for converting the voltage sums,derived from the respective adder means, to A.C. signals proportional tothe degree to which said first-named pattern matches said referencepattern, means in the paths of the respective A.C. signals for weightingsaid A.C. signals in accordance with the relative importance of thepattern segments represented thereby, and means common to the outputcircuits of fall of said weighting means for registering a valueindicative of the sum of all said weighted A.C. signals.

4. A system as defined in claim 3, including relayoperated switch meansresponsive to cessation of signal input to de-activate said registeringmeans.

5. A system as defined in claim 3, wherein said weighting means includesmeans for compensating each A.C. signal to a degree proportional to thedegree of matching, thereby rendering said signals independent of theaverage magnitude of the input voltages.

6. In electronic pattern-matching or correlation, a plurality of D.C.circuits specifying a distribution, adder means common to said D.C.circuits for measuring their average voltage, means forming part of saidadder means for reversing the polarity of said mean or average voltage;means including a plurality of signal correlator units for matching theset of D.C. voltages, with the mean or average voltage having reversedpolarity, in a reference pattern specifying voltage ratios with respectto the mean or average, and voltage divider means in the output paths ofsaid signal correlator units for detecting the extent ofpattern-matching between the set of D.C. voltages and the referencepattern.

References Cited in the file of this patent UNITED STATES PATENTS Re.24,670 Smith July 21, 1959 2,167,124 Minton July 25, 1939 2,243,527Dudley May 27, 1941 2,446,188 Miller Aug. 3, 1948 2,530,693 Green Nov.21, 1950 2,557,581 Triman June 1.9, 1951 2,575,909 Davis Nov. 20, 195110 Malthaner Apr. 20, 1954 Bennett Apr. 20, 1954 Smith June 1, 1954Burgett June 19, 1954 Biddulph Aug. 3, 1954 Whitehead July 26, 1955McFee Mar. 12, 1957 Gordon et a1. July 26, 1957 Piety June 17, 1958 KuckAug. 26, 1958 Smith Aug. 25, 1959 Raisbeck Oct. 13, 1959 Lehman Nov. 3,1959

